A three-dimensional ("3D") vision endoscope or microscope, hereinafter referred to as a "stereo" endoscope or microscope, comprises a stereoscopic optical system for forming a 3D image of an object. The stereoscopic optical system comprises objective lens means arranged to pick up two slightly different images of a object that approximate the two views (left and right) provided by human binocular vision. The difference between the two views is known as parallax. By properly aligning and presenting the two optical target images to human binocular vision, a three-dimensional sense of the target is presented to the viewer.
In the case of a conventional (non-electronic) optical endoscope or microscope the two optical target images picked up by the objective lens means are passed to a viewing system in the form of a binocular eyepiece unit comprising two like optical channels each having, inter alia, a focusing lens followed by an ocular lens. In the case of an electronic stereo endoscope or microscope, the images picked up by the objective lens means are passed to an electronic stereo camera. As used herein the term "electronic stereo camera" is intended to denote a camera comprising two solid state electronic imaging devices, typically charge coupled devices (CCD's), that are capable of generating electrical output signals representative of images received thereby. The camera may also include electronic circuit means for controlling operation of the imaging devices so as to produce said output signals. Alternatively, some or all of said electronic circuit means may be disposed outside of the camera. The camera may also comprise image formation optics for relaying images and focusing them on the imaging devices. Also as used herein the term "video camera head" is intended to designate a camera having a single electronic imaging device, with or without associated electronic circuit means for controlling its operation so as to produce a useful output signal representative of the images received by said imaging device. Hence a stereo video camera essentially comprises two video cameras heads. The video camera head also may also comprise image formation optics for relaying images and focusing them on the imaging device.
The output signals of the electronic imaging devices are processed to provide video signals that in turn are used to drive an electronic viewing (display) system. The latter may comprise a conventional video monitor that is operated so as to provide a stereoscopic display in response to the video signals, the stereoscopic display typically being generated so as to be viewable by special polarized spectacles or, in the case where left and right images are displayed alternately, by spectacles having shutters that alternately block each eye in synchronism with alternate displaying of the left and right images. The viewing system also may be a head-mounted display unit, comprising first and second miniature electronic display devices, one for each eye, that display the left and right images respectively. The form of display system used is not critical to the invention.
The capability of the human brain to fuse two images to produce a three-dimensional visual effect is tolerant of misalignment errors between the two images. However, only a small degree of misalignment, in the form of differences in image size, vertical position and rotation, will cause viewer discomfort, and such discomfort increases as a function of the degree of misalignment. Consequently prolonged viewing of misaligned stereo images, such as occurs in cardiac surgery or pneurosurgery operations, can produce a high degree of viewer discomfort.
In the optical domain, it is possible to align images by physically moving lenses, prisms, CCD's and other optical devices. However, in the case of a stereo endoscope the size limitation on the insertion portion of the endoscope results in the optical elements being quite small, making it difficult to mechanically adjust components to correct for misalignment errors.
U.S. Pat. No. 5,577,991, issued Nov.26, 1996 to N. Akui et al, discloses various methods for adjusting left and right images to correct for mismatch. FIG. 3 of that patent discloses a method and apparatus for electronically correcting for optical mismatch errors, while other figures of that patent show mechanical means for optical systems of images. Mechanical methods and means for correcting for misalignment errors of the type described are expensive and are not fully satisfactory for a number of reasons. The electronic method embodied in the system of FIG. 3 of said patent is not explained or illustrated in specific detail but appears to have certain limitations. Nevertheless, it is recognized that the equivalent of horizontal and vertical image shift, image size change, and image rotation can be performed very effectively in the electronic domain.